It is known from EP-A-0 164 564 to use an excimer laser to produce blind holes in a laminate with the layer sequence metal-dielectric-metal. The uppermost metal layer of the laminate is in this case used as an aperture mask, the pattern of holes of which is transferred by means of photolithography and is produced by subsequent etching. The dielectric exposed in the region of the apertures of this mask is then removed by the action of the excimer laser until the lowermost metal layer is reached and the removal process is ended. The known method is used in particular in the manufacture of multilayer printed circuit boards for producing the required plated-through holes in the form of blind holes.
The German periodical “Feinwerktechnik & Messtechnik 91 (1983) 2, pages 56-58, discloses a similar method of manufacturing multilayer printed circuit boards, in which the blind holes serving as plated-through vias are produced with the aid of a CO2 laser. Here, too, the uppermost copper foil serves as an aperture mask, with which the copper is etched away whereever the laser beam is intended to produce a hole.
DE-A-197 19 700 also already discloses devices for the laser drilling of laminates, in which a first laser with a wavelength in the range from approximately 266 nm to 1064 nm is used for drilling the metal layers and a second laser with a wavelength in the range from approximately 1064 nm to 10600 nm is used for drilling the dielectric layers.
U.S. Pat. No. 5,593,606 discloses a method for the laser drilling of laminates in which a single UV laser, the wavelength of which lies below 400 nm and the pulse widths of which lie below 100 ns, is used for drilling the metal layers and for drilling the dielectric layers. Precluding the use an excimer laser, metal and organic material are consequently drilled with the same UV laser.
DE-A-198 24 225 discloses a further method for the laser drilling of laminates, in which for example an SHG (second harmonic generation) YAG laser with a wavelength of 532 nm or a THG (third harmonic generation) YAG laser with a wavelength of 355 nm can also be used for drilling the metal layers and for drilling the dielectric layers.
In principle, it can be stated that, in the laser drilling of organic materials with UV lasers, that is to say with wavelengths below 400 nm, a photochemical decomposition of the organic materials takes place. Consequently, no burning occurs and, on account of the extremely small or non-existent thermal loading, in the case of laminates no delamination occurs. By contrast with this, in the laser drilling of organic materials with CO2 lasers, a thermal decomposition of the organic materials takes place, that is to say burning may occur and, in the case of laminates, there is the risk of delamination. In comparison with UV lasers, however, considerably shorter machining times can be achieved with CO2 lasers in the drilling of organic materials.
EP-A-0 478 313 discloses the so-called SLC (Surface Laminar Circuit) method, in which initially a first wiring level is produced on a base substrate. Then, a dielectric layer of a photosensitive epoxy resin is applied to this first wiring level by screen printing or by curtain coating. Then, blind holes are produced in the dielectric layer by photolithographic means, by exposing and developing. After the chemical and electrolytic copper-plating of the walls of the holes and the surface of the dielectric layer, the second wiring level is produced by structuring of the deposited copper layer. Further wiring levels can be produced in the way described by the alternating application of photosensitive dielectric layers and copper layers.